(a) Technical Field
The present invention relates to a catalyst used for steam carbon dioxide reforming of natural gas, wherein an alkaline earth metal alone or an alkaline earth metal and a group 8B metal are supported on a hydrotalcite-like catalyst containing nickel, magnesium and aluminum.
(b) Background Art
With the recent surging oil prices, interests in alternative energy are increasing day by day. In particular, preparation of synthetic fuels using natural gas buried in stranded gas fields is becoming more important as a new source of energy. The reforming reaction for preparing synthesis gas from natural gas is achieved by reforming of methane, which is the main component of natural gas.
The reforming reactions for preparing synthesis gas from natural gas can be classified into steam reforming (SR), partial oxidation (POX), autothermal reforming (ATR), carbon dioxide reforming (CDR), steam carbon dioxide reforming (SCR), tri-reforming (TriR) or the like.Steam reforming (SR): CH4+H2O→3H2+CO  {circle around (1)}Partial oxidation (POX): CH4+0.5O2→2H2+CO  {circle around (2)}Autothermal reforming (ATR): CH4+0.5O2+H2O→3H2+CO2  {circle around (3)}Carbon dioxide reforming (CDR): CH4+CO2→2H2+2CO  {circle around (4)}Steam carbon dioxide reforming (SCR): 2CH4+H2O+CO2→5H2+3CO  {circle around (5)}Tri-reforming (TriR): 3CH4+H2O+0.5O2+CO2→7H2+4CO  {circle around (6)}
As seen from the above reaction formulas, since the synthesis gas produced from each reforming reaction has a different molar ratio of carbon monoxide to hydrogen, the synthesis gases prepared from different reforming reactions are used for different applications.
At present, methods for preparing synthesis gases whose H2/CO molar ratios can be controlled variously through reforming of methane are studied variously. Among them, CDR is drawing a lot of attentions because it utilizes carbon dioxide as reactant. However, since the CDR reaction has a fatal problem that the catalyst is deactivated due to carbon deposition, the steam carbon dioxide reforming (SCR) which combines SR and CDR was provided to solve the problem [Chem. Rev. 2007, 107, 3952-3991]. A method of controlling the H2/CO molar ratio of a synthesis gas in the SCR reaction by controlling the molar ratio of reactants CH4/CO2/H2O and the recirculation ratio of unreacted reactants was reported [Korean Patent No. 10-1068995].
A floating, production, storage and offloading (FPSO) facility is a floating energy plant which is superior in durability and safety as compared previous floating facilities. The FPSO unit includes an apparatus for drilling crude oil and an apparatus for separating the crude oil in glassy oil state from associated gas. The FPSO unit also includes an apparatus for storing the crude oil and an apparatus for offloading the crude oil to a means for transporting the crude oil. The associated gas produced along with the oil in the oil-FPSO process is either burnt off and released into the atmosphere or compressed and then reinjected into the oil wells. Thus, the GTL-FPSO, DME-FPSO or MeOH-FPSO process may be considered to utilize the associated gas from the oil fields as a raw material in the gas-to-liquids (GTL) process after preparing a synthesis gas aboard the FPSO. In particular, it is important to develop an economical and compact process to convert the gas from offshore oil fields and stranded gas fields into a synthetic fuel with minimized investment and operation costs. Since the gas pressure at the offshore oil fields or stranded gas fields is about 80 bar and synthesis of dimethyl ether, Fischer-Tropsch synthesis or synthesis of methane following reforming occurs at 20 bar or above, it is desirable that the reforming process occur in a pressure range of 20-80 bar to achieve a compact, economical process.
As a catalyst for steam carbon dioxide reforming (SCR) of natural gas, a nickel-based catalyst wherein nickel (Ni) is supported as an active component on a Ce/Mg—Al or Ce—Zr/Mg—Al support is commonly used [Korean Patent No. 991,263]. The catalyst disclosed in Korean Patent No. 991,263 is used under a low-pressure condition of around the atmospheric pressure and is known to exhibit very low catalytic activity at high pressures of 20 bar or above.
Thus, the inventors of the present invention have made efforts to develop a novel catalyst which can be used not only under an atmospheric pressure condition but also under a high pressure condition of 20-80 bar to prepare a synthesis gas having an H2/CO molar ratio of approximately 1-2.2 by steam carbon dioxide reforming (SCR) of natural gas, particularly a synthesis gas having an H2/CO molar ratio of 1.8-2.2 which is appropriate for Fischer-Tropsch synthesis or methanol synthesis.